A seat drive device for selectively actuating a plurality of position adjustment mechanisms by a single drive motor is disclosed in JP-A-2013-107624. According to such a seat drive device, four position adjustments (the front-rear adjustment and up-down adjustment of a seat, the reclining angle adjustment of a seat back, and the tilt angle adjustment of a seat cushion) can be performed by using a single drive motor. Therefore, a clutch mechanism is provided in each path for distributing the output of the drive motor to each position adjustment mechanism. Then, by setting a clutch corresponding to a mechanism that performs the position adjustment to a connected state, the output of the drive motor is transmitted to the corresponding position adjustment mechanism. On the other hand, by setting a clutch corresponding to a mechanism that does not perform the position adjustment to a non-connected state, the output of the drive motor is not transmitted to the corresponding position adjustment mechanism.
Although each position adjustment mechanism is individually operated in principle, a plurality of position adjustment mechanisms can be simultaneously operated depending on the manner of operation. However, the specification of the drive motor is determined on the premise that it operates one position adjustment mechanism. Therefore, when a plurality of position adjustment mechanisms is simultaneously operated, there is a problem that the drive motor is overloaded and the operation speed is lowered.